Something was setting LC_ALL in my Ubuntu 22.04 desktop environment. Terminals were unaffected but desktop apps were apparently using the default C locale with 'US style' date formatting. There were also numerous log entries like this:
snapd-desktop-integration.snapd-desktop-integration[5623]: /bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.utf8)
According to sources online, LC_ALL shouldn't be set. I looked for the source of the command. There was nothing in any of the scripts in my $HOME (such as .profile, .bashrc). I created a brand new user and the same issues were there when logged into their account's desktop. I looked in /etc/profile.d which contains system defaults for user profile settings.
To find out what files in the profile directory were installed by a package:
$ for file in `ls /etc/profile.d/`; do dpkg --search $file; done
base-files: /etc/profile.d/01-locale-fix.sh